Infrastructure has grown rapidly as an alternative asset class, yet many of the complex processes that transform public infrastructures into lucrative financial assets are poorly understood. This article examines investments by an infrastructure debt fund, to show how financial innovations expand and diversify the infrastructure asset class by finding new ways to generate financial returns from infrastructures. Infrastructure debt is an emerging sector of the infrastructure asset class, where private debt funds create assets that generate returns by extending loans or bond financing to physical infrastructures. The analysis uses assetization as a conceptual framework to scrutinise the construction of financial assets, centring the role of rent generation and extraction to show how infrastructure debt funds create financial value. By bringing the performative work of asset construction into dialogue with the political-economic forces enabling rent extraction, the analysis augments existing literature on financialized infrastructures. The findings show how infrastructure debt assets are predicated on multiple rounds of assetization: initially, the essential nature of infrastructure services is exploited to generate and extract monopoly rents as long-term revenue streams, and in turn, debt funds extend claims on these revenue streams to extract rents through interest payments. In this way, infrastructure debt extends the infrastructure asset class and provides a new route to extract rents, raising concerns over the potential of these investment practices to contribute to inclusive regional development and just transitions to mitigate and adapt to climate change.